• Mark Lenz, Ladina Hofmann-Fliri, Lena Anna Kasper, Peter Varga, Ivan Zderic, Dominic Gehweiler, Kajetan Klos, Gunther O Hofmann, Karl Stoffel, and Boyko Gueorguiev.
• AO Research Institute Davos, Switzerland; Department of Trauma, Hand and Reconstructive Surgery, University Hospital Jena, Germany. Electronic address: lenzmar@web.de.
• Injury. 2021 Jan 1; 52 (1): 53-59.

IntroductionSlotted nails allow a connection to a total hip arthroplasty (THA) stem and act as intramedullary load carrier. This study compares construct stiffness, cycles to failure and failure load between a retrograde slotted femur nail construct docked to a THA stem and a lateral locking plate in a human periprosthetic femur fracture model.Materials And MethodsIn seven pairs of fresh-frozen human anatomic femora with cemented THA, a transverse osteotomy was set simulating a Vancouver type B1 fracture. The femora were instrumented pairwise with either a retrograde slotted nail coupled to the prosthesis stem, or a locking plate plus a locking attachment plate. Four-point mediolateral bending, torsional and axial bending construct stiffness was investigated via non-destructive tests. Cyclic testing under progressively increasing physiologic loading was performed at 2 Hz until catastrophic construct failure.ResultsMediolateral bending stiffness did not differ significantly between the two groups (P=0.17) but exhibited a biphasic profile with significantly increased stiffness in both groups (P<0.01). Nail constructs provided a significantly lower torsional stiffness (0.49 ± 0.66 Nm/°) than plate constructs (1.70 ± 0.86 Nm/°), P=0.03. Axial bending stiffness did not differ significantly between the groups (Nail: 605 ± 511 N/mm; Plate: 381 ± 428 N/mm), P=0.61. Cycles to failure and failure load were significantly higher for the plate constructs (25'700 ± 8'341; 3'070 ± 1334 N) compared with the nail constructs (20'729 ± 7'949; 2'573 ± 1295 N), P=0.04.ConclusionThe docking nail construct provides an intramedullary fixation with connection to the prosthesis stem; however, it is biomechanically weaker in stable fractures compared to the plate construct.Copyright © 2020. Published by Elsevier Ltd.

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